I received a brand new GTX680 (my third one now) from Galaxy today. Also in the box was a pre-paid shipping label to send the other one (the first replacement) back.

From what I can tell, the new card seems to work perfectly. I ran Unigine Heaven for about an hour, then played an hour's worth of BF3, and there are no problems to report.

So, although it took a little while and a few tries, Galaxy managed to take care of me to my satisfaction and I am a happy customer.

It's especially important as the problem I was having was an odd one (crashing in some programs, but fine in others) and was not easily replicable by their techs. So, they took me on my word and helped me out.